1. Field of the Invention
The present invention relates to filter circuits that include inductors connected in a T-shaped pattern.
2. Description of the Related Art
In the related art, a variety of filter circuits that include inductors have been designed. FIG. 1 is a circuit diagram illustrating a filter circuit described in Japanese Unexamined Patent Application Publication No. 2007-129565. The filter circuit illustrated in FIG. 1 is a T-circuit low pass filter in which two inductors L11 and L12 are connected in series with each other and in which a point between these two inductors is connected to the ground via an inductor L13 and a capacitor C. The filter circuit illustrated in FIG. 1 includes inner layer electrode patterns of a multilayer body formed by stacking a plurality of dielectric layers on top of one another.
The filter circuit described in Japanese Unexamined Patent Application Publication No. 2007-129565 is configured such that the inductor L12 and the inductor L13 are provided on different layers with a ground electrode layer interposed therebetween in order to prevent the inductance of the inductor L13 from changing due to the inductor L12 and the inductor L13, which are disposed close to each other, becoming electromagnetically coupled with each other. Thus, the inductance of the inductor L13 is prevented from changing and it is possible to provide a low pass filter having desired frequency characteristics.
However, when a multilayer body is constructed by stacking dielectric layers on top of one another, since misalignment sometimes occurs between the dielectric layers, there is a risk of the inductances of the inductors L11, L12 and L13 described in Japanese Unexamined Patent Application Publication No. 2007-129565 being changed. For example, when the inductor L11 is provided in an upper layer portion of the multilayer body and the inductor L12 is provided in a lower layer portion of the multilayer body, if a misalignment occurs in the upper layer portion, just the inductance of the inductor L11 will change.
Consequently, there is a risk that the inductance ratio between the inductors L11, L12 and L13 will change and be significantly shifted from the inductance ratio for the desired filter characteristics. In addition, there is a risk that the mutual inductance will be changed by a deviation in the distance between the inductors L11, L12 and L13 and that this will affect the filter characteristics.